1. Field of the Invention
The present invention relates to a RFID (Radio_Frequency_Identification) tag which exchanges information with an external device without contacting the device. Among persons skilled in the art of the field of the invention, the RFID tag used in the invention may also be called a “Wireless IC tag”.
2. Description of the Related Art
Recent years there have been proposed various RFID tags which exchange information with an external device typified by a reader and writer using a radio wave without contacting the device (for example, see Japanese Patent Laid-Open Nos. 2000-311226, 2000-200332 and 2001-351082). One such RFID tag is provided with an antenna pattern for radio communication and a circuit chip both mounted on a base sheet made of a plastic or paper. Applications for such a RFID tag include discriminations of an article attached to the RFID tag through exchange of information of the article with an outside device.
The temperature resistance of a circuit chip mounted in such a RFID tag is guaranteed at best for a ten-year usage under an environment of 55° C. Under an environment of over such guaranteed temperature, there arises a problem that the reliability is deteriorated.
Typical of the RFID tag methods of protecting an object from a high temperature environment include thermal insulating methods such as vacuum insulation that the object to be protected is enclosed in a vacuum and hollow metal case to shield entrance of heat to the object, and covering the object with a thermal insulating material, for example a polystyrene foam.
In the vacuum insulation described above, however, an antenna pattern connected to a circuit chip is encased together with the circuit chip in a metal case, thereby causing radio communication with the antenna pattern to be obstructed by the metal case. In addition, because a polystyrene foam, a general thermal insulating material, has a low thermal capacity, the temperature inside the metal case may exceed the temperature guaranteed for a circuit chip when left in a high temperature for a long time.
The invention has been made in a view of the above circumstances and provides a RFID tag which is capable of tolerating a high temperature environment.